Multiplicity Distributions Of Hadrons Research Articles

Effects of saturation and fluctuating hotspots for flow observables in ultrarelativistic heavy-ion collisions

We investigate the effects of saturation dynamics on midrapidity flow observables by adding fluctuating hotspots into the novel Monte Carlo EKRT (MC-EKRT) event generator for high-energy nuclear collisions. We demonstrate that the intensity of the saturation effects significantly affects the ratio between the flow coefficients v3 and v2 at the LHC. Adding a hotspot substructure to the nucleons enhances the saturation effects and improves the agreement with the measured data. We show that the collision-energy dependence of the flow coefficients obtained using the MC-EKRT initial states with hotspots is improved in comparison with the earlier event-by-event EKRT model. In addition, we present the results for the charged hadron multiplicity distribution in Pb+Pb collisions at the LHC, and show that the minijet multiplicity originating fluctuations of the saturation scale included in MC-EKRT, as well as the presence of hotspots, are necessary for describing the measured large-multiplicity tail in the distribution. Published by the American Physical Society 2024

The U-Matrix geometrical model for multi-particle production in high-energy hadronic collisions

Inspired by the picture portraying the KNO scaling violation as an extension of the geometrical scaling violation, the current study proposes a phenomenological model for multi-particle production in hadron collisions based on the geometrical approach and using the U-Matrix unitarization scheme of the scattering amplitude. The model has been fine-tuned and all parameters have been derived from optimal fits to various hadronic multiplicity distributions data in p + pp¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ p\\left(\\overline{p}\\right) $$\\end{document} collisions across a broad range of energies. The results have revealed that our model furnishes a reasonable description of diverse multiplicity distributions at various energies. Besides, they have demonstrated a pronounced violation of the geometrical scaling, which eventually resulted in a significant violation of the KNO scaling. The study has also analyzed the higher-order moments of the multiplicity distribution. We have observed an unexpected overestimation of the fluctuations and correlations between final state particles with increasing energy, particularly above LHC energy. It is claimed that this overestimation is due to statistical fluctuations embedded in the U-matrix scheme. The findings of this study have shed light on the key role of the U-matrix scheme in the impact of collision geometry on multi-particle production processes at high energy.

Scale dependence of the q and T parameters of the Tsallis distribution in the process of jet fragmentation

The dependence of the q and T parameters of the Tsallis-distribution-shaped fragmentation function (FF) on the fragmentation scale (found to be equal to the jet mass) is calculated via the resummation of the branching process of jet fragmentation in the leading-log appriximation (LLA) in the $$\phi ^3$$ theory. Jet and hadron spectra in electron-positron ( $$e^+e^-$$ ) annihilations with 2- and 3-jet final states are calculated using virtual leading partons. It is found that jets, produced earlier in the branching process, are more energetic, and the energy, angle and multiplicity distributions of hadrons stemming from them are broader. It is also found that replacing the LL resummation in the branching process by a single splitting provides good approximation for the jet energy distribution in 2-jet events. Furthermore, a micro-canonical statistical event generator is presented for the event-by-event calculation of hadron momenta in $$e^+e^-$$ annihilations.

Jet fragmentation properties with CMS open-data

The CMS collaboration has made some of their data public, making it possible for external users to perform physics analysis using real data. In this work, we report the measurement of jet properties such as fragmentation function, and the average multiplicity distribution of leptons and charged hadrons within the jets, all of them produced in pp collisions at = 7 TeV. We show that by implementing high energy cuts, the uncorrected experimental data approaches the behavior of corrected data, facilitating the use of open-data for simple analysis. The analysis is restricted in pseudorapidity and energy of the jets to: ∣η Jet∣ < 2.1 and E Jet > 120 GeV respectively. For the study we used the anti − K T algorithm applied to four samples of 2011 CMS open-data, to explore the possible differences obtained by using different trigger conditions, and the results are compared with predictions from the Pythia 8 event generator.

Oscillations in Modified Combinants of Hadronic Multiplicity Distributions

Oscillations in modified combinants (C_jCjs) have been of interest to multiparticle production mechanisms since the 1990s [1]. Recently, there has been a discussion on how these oscillations can be reproduced by compounding a binomial distribution with a negative binomial distribution [2,3]. In this work, we explore a stochastic branching model based on a simple interaction term \lambda\overline{\psi}\phi\psiλψ¯ϕψ for partons and propose a hadronization scheme to arrive at the final multiplicity distribution. We study the effects that compounding our model with a binomial distribution has on C_jCjs and explore its physical implications. We find that there is a significant difference in the oscillations in C_jCjs between high energy pp and p\bar{p}pp‾ scattering that our model can reproduce.

Multiplicity and pseudo-rapidity density distributions of charged particles produced in pp, pA and AA collisions at RHIC & LHC energies

Multiplicity and pseudorapidity (η) density (dN ch/dη) distributions of charged hadrons provide key information towards understanding the particle production mechanisms and initial conditions of high-energy heavy-ion collisions. However, detector constraints limit the η-range across which charged particle measurements can be carried out. Extrapolating the measured distributions to large η-range by parameterizing measured distributions and by using calculations from event generators, we characterize the production of charged particles over the full kinematic range. In the present study, we use three different anstze to obtain quantitative descriptions of the shape of pseudorapidity distributions of charged hadrons produced in pp, p–A, and A–A collisions for beam energies () ranging from a few GeV to a few TeV corresponding to RHIC and LHC energies. We study the limiting fragmentation behavior in these collisions and report evidence for participant-scaling violations in high-energy collisions at the TeV scale. We additionally examine measured pseudorapidity distributions to constrain models describing initial conditions of particle production. We predict the centrality dependence of charged particle multiplicity distributions at FAIR and NICA energies and give an estimation of charged particle multiplicity at η = 0 for the proposed HE-LHC and FCC energies.

Probing the Neutron Skin with Ultrarelativistic Isobaric Collisions.

Particle production in ultrarelativistic heavy ion collisions depends on the details of the nucleon density distributions in the colliding nuclei. We demonstrate that the charged hadron multiplicity distributions in isobaric collisions at ultrarelativistic energies provide a novel approach to determine the poorly known neutron density distributions and thus the neutron skin thickness in finite nuclei, which can in turn put stringent constraints on the nuclear symmetry energy.

Data structure in the HIJING 2.0 Monte Carlo program

The Heavy-Ion Jet Interaction Generator (HIJING) Monte Carlo model was developed to simulate hadron production in proton–proton, proton–nucleus and nucleus–nucleus collisions. It has been updated recently with the latest parton distributions functions (PDFs) and new set of the parameters in the two-component mini-jet model that controls total [Formula: see text] cross-section and the central pseudorapidity density. We will discuss these new elements in the HIJING 2.0 model, derive the two-component model from the eikonal formalism of hadron–hadron collisions and review the hadron spectra and multiplicity distributions as compared to recent experimental data at the LHC energies. We will review in particular the data structure of the Monte Carlo program and discuss future improvements.

Multiphase transport model predictions of isobaric collisions with nuclear structure from density functional theory

Isobaric $^{96}_{44}$Ru+$^{96}_{44}$Ru and $^{96}_{40}$Zr+$^{96}_{40}$Zr collisions were performed at the Relativistic Heavy Ion Collider in 2018. Using the "a multi-phase transport" model with nuclear structures calculated by the density functional theory (DFT), we make predictions for the charged hadron multiplicity distributions and elliptic azimuthal anisotropies in these collisions. Emphases are put on the relative differences between the two collision systems that can decisively discriminate DFT nuclear distributions from the commonly used Woods-Saxon densities.

Multifractal characteristics of multiparticle production in heavy-ion collisions at SPS energies

Entropy, dimensions and other multifractal characteristics of multiplicity distributions of relativistic charged hadrons produced in ion–ion collisions at SPS energies are investigated. The analysis of the experimental data is carried out in terms of phase space bin-size dependence of multiplicity distributions following the Takagi’s approach. Yet another method is also followed to study the multifractality which, is not related to the bin-width and (or) the detector resolution, rather involves multiplicity distribution of charged particles in full phase space in terms of information entropy and its generalization, Rényi’s order-[Formula: see text] information entropy. The findings reveal the presence of multifractal structure — a remarkable property of the fluctuations. Nearly constant values of multifractal specific heat “[Formula: see text]” estimated by the two different methods of analysis followed indicate that the parameter “[Formula: see text]” may be used as a universal characteristic of the particle production in high energy collisions. The results obtained from the analysis of the experimental data agree well with the predictions of Monte Carlo model AMPT.

More Results from the Opera Experiment at the Gran Sasso Underground Lab

The OPERA experiment reached its main goal by proving the appearance of [Formula: see text] in the CNGS [Formula: see text] beam. Five [Formula: see text] candidates fulfilling the analysis defined in the proposal were detected with a S/B ratio of about ten allowing to reject the null hypothesis at 5.1[Formula: see text]. The search has been extended by loosening the selection criteria in order to obtain a statistically enhanced, lower purity, signal sample. One such interesting neutrino interaction with a double vertex topology having a high probability of being a [Formula: see text] interaction with charm production is reported. Based on the enlarged data sample the estimation of [Formula: see text][Formula: see text] in appearance mode is presented. The search for [Formula: see text] interactions has been extended over the full data set with a more than twofold increase in statistics with respect to published data. The analysis of the [Formula: see text] channel is updated and the implications of the electron neutrino sample in the framework of the 3+1 neutrino model is discussed. An analysis of [Formula: see text] interactions in the framework of the sterile neutrino model has also been performed. Finally, the results of the study of charged hadron multiplicity distributions is presented.

Jet mass dependence of fragmentation in positron-proton collisions

We propose the characterization of fragmentation functions by the energy fraction x, a hadron takes away from the energy of the jet measured in the frame co-moving with the jet. Besides, we propose the usage of the jet mass as the fragmentation scale Q. We show that these two Lorentz-invariant variables emerge naturally in a microcanonical ensemble with conserved fourmomentum. Then, we construct a statistical hadronisation model, in which, two features of the hadronic final states in various high-energy reactions (power law spectra and negative-binomial multiplicity distributions) can be connected simply. Finally, we analyse the scale dependence of the parameters of the model (power of the spectrum and mean energy per hadron) in the phi^3 theory. Fitting fragmentation functions in diffractive positron-proton collisions, we obtain a prediction for the jet mass dependence of the hadron multiplicity distribution inside jets.

How many of the scaling trends inppcollisions will be violated atsNN=14 TeV? Predictions from Monte Carlo quark-gluon string model

Multiplicity, rapidity and transverse momentum distributions of hadrons produced both in inelastic and nondiffractive $pp$ collisions at energies from $\sqrt{s} = 200$\,GeV to 14\,TeV are studied within the Monte Carlo quark-gluon string model (QGSM). Good agreement with the available experimental data up to $\sqrt{s} = 13$\,TeV is obtained, and predictions are made for the collisions at top LHC energy $\sqrt{s} = 14$\,TeV. The model indicates that Feynman scaling and extended longitudinal scaling remain valid in the fragmentation regions, whereas strong violation of Feynman scaling is observed at midrapidity. The Koba-Nielsen-Olesen (KNO) scaling in multiplicity distributions is violated at LHC also. The origin of both maintenance and violation of the scaling trends is traced to short range correlations of particles in the strings and interplay between the multistring processes at ultrarelativistic energies.

Charged Hadron Multiplicity Distribution at Relativistic Heavy-Ion Colliders

The present paper reviews facts and problems concerning charge hadron production in high energy collisions. Main emphasis is laid on the qualitative and quantitative description of general characteristics and properties observed for charged hadrons produced in such high energy collisions. Various features of available experimental data, for example, the variations of charged hadron multiplicity and pseudorapidity density with the mass number of colliding nuclei, center-of-mass energies, and the collision centrality obtained from heavy-ion collider experiments, are interpreted in the context of various theoretical concepts and their implications. Finally, several important scaling features observed in the measurements mainly at RHIC and LHC experiments are highlighted in the view of these models to draw some insight regarding the particle production mechanism in heavy-ion collisions.

CGC predictions for [formula omitted] collisions at the LHC and signature of QCD saturation

We present various predictions for the upcoming p+Pb collisions at S=5 TeV within the color glass condensate (CGC) formalism, including single inclusive charged hadron production, single inclusive prompt photon production, direct photon production, charged hadron multiplicity distribution and photon–hadron azimuthal correlations. Using the running-coupling Balitsky–Kovchegov evolution equation for calculating various observables, we show that the main source of uncertainties is due to less constrained initial nuclear saturation scale. This gives rise to rather large theoretical uncertainties for nuclear modification factor RpA at the LHC. Nevertheless, we propose a simple scheme in which one can still test the main dynamics of the CGC/saturation in p+A collisions at the LHC.

VOID PROBABILITY ENHANCED MULTIPLICITY DISTRIBUTION OF PRODUCED HADRONS IN p–p COLLISION AT LHC ENERGIES

This paper studies the multiplicity distribution of hadrons produced in p–p collisions at 0.9 and 2.36 TeV using ALICE as a detector. The multiplicity distribution exhibits enhanced void probability. They are also found to satisfy the void probability scaling. The scaling of χ with [Formula: see text] is studied using the generalized hypergeometric model. The variation of the parameter "a" of the hyper geometric model with energy and type of events is also studied. The parameter "a" distinguishes between various theoretical models, e.g. Lorentz/Catalan, negative binomial, geometric distribution etc. Finally a comparison is made with the [Formula: see text] collisions at 200, 546 and 900 GeV. It is observed both for p–p and [Formula: see text] data, the value of "a" decreases with increase in collision energy and approach towards the upper bound or the NB model of the void probability scaling.

Particle Production in pA Collisions and QCD Saturation

The forthcoming LHC measurements in proton-nucleus (pA) collisions at forward rapidities can discriminate between the color glass condensate (CGC) and alternative approaches including standard collinear factorization one. We report some of our recent predictions based on gluon saturation/CGC formalism for pA collisions at the LHC including the charged hadron multiplicity distribution, the nuclear modification factor for single inclusive hadron and prompt photon production, and the azimuthal angle correlation of the semi-inclusive hadron-photon production.

Parton Rescattering Effect on the Charged Hadron Forward-Backward Multiplicity Correlation in pp Collisions at √s = 200 GeV

The parton rescattering effect on the charged hadron forward-backward multiplicity correlation in pp collisions at √s = 200 GeV is studied by a parton and hadron cascade model, PACIAE, based on the PYTHIA model. The calculated multiplicity and pseudorapidity distribution of the final state charged hadrons are well compared with the experimental data. It is found that the final state charged hadron pseudorapidity distribution is different from the initial state charged partons. The parton rescattering effect on the charged hadron forward-backward multiplicity correlation increases with the increasing parton rescattering strength in the center pseudorapidity region (|η| < 1). However, this effect becomes weaker in the outer pseudorapidity region (|η| > 1).

Gluon saturation inpAcollisions at energies available at the CERN Large Hadron Collider: Predictions for hadron multiplicities

The upcoming $p+\text{Pb}$ run at the Large Hadron Collider (LHC) will probe the nuclear gluon distribution at very small Bjorken $x$ (from $x\ensuremath{\sim}{10}^{\ensuremath{-}4}$ at midrapidity down to $x\ensuremath{\sim}{10}^{\ensuremath{-}6}$ in the proton fragmentation region) and will allow testing of approaches based on parton saturation. Here, we present the predictions of the Kharzeev-Levin-Nardi model for hadron multiplicities and multiplicity distributions in $p+\text{Pb}$ collisions at a center-of-mass energy of 4.4 TeV. We also compare the model to the existing $pp$, $dA$, and $AA$ data from the Relativistic Heavy Ion Collider and LHC.

Two-component model in quantum statistical framework compared with multiplicity distributions in proton–proton collisions at energies up to [formula omitted

Proton–proton collisions at new high energies (s=2.36 and 7 TeV) at LHC resulted into greater mean multiplicities (〈n〉) of charged particles in the mid-rapidity region than estimated ones by different models and event generators. Another significant observation in multiplicity data is the change in slope in the distribution of primary charged hadrons in symmetric pseudorapidity interval |η|<2.4. The change is most prominent with data at s=7 TeV. These new observations merit further studies. We consider a two-component model of particle production to analyze multiplicity distributions of charged hadrons from proton–proton collisions at centre-of-mass energies s=0.9, 2.36 and 7 TeV in symmetric pseudorapidity intervals |η| of increasing width around the centre-of-mass pseudorapidity ηcm=0. The model, based on Quantum Statistical (QS) formalism, describes multiplicity distribution by convolution of a Negative Binomial Distribution (NBD), representing a chaotic component, and a Poisson Distribution (PD), representing a coherent component of particle productions. The behaviour of characteristic parameters of the model is followed by the LHC data, while a scaling law, involving information entropy in quantum statistical viewpoint and derived as a function of chaotic multiplicity obtained from the two-component model, is not obeyed by the data, satisfactorily. An attempt to match the measured multiplicity distributions and suggested convolutions with values of characteristic parameters extracted from the data confirms disagreement between the data and the model.